Chinese scientists have expressed concern after detecting another new strain of flu that has the potential to become a pandemic.
The newly emerged flu virus is carried by pigs, but can infect humans and transmit from human to human, they say.
The researchers expressed their concern that it could mutate further so that it can spread easily from person to person, and trigger a global outbreak, reports BBC.
Although it is not an immediate problem, they say, it has "all the hallmarks" of being highly adapted to infect humans and requires close monitoring.
As it is a new type of virus, people could have little or no immunity to it, the scientists said.
Measures to control the virus in pigs, and close monitoring of swine industry workers, should be swiftly implemented, they wrote in the journal Proceedings of the National Academy of Sciences.
New Pandemic threat
When the world is struggling with Covid-19 pandemic, experts have been watching for a new strain of influenza is among the top disease threats.
Earlier in 2009, a swine flu outbreak began in Mexico- but that was less deadly than initially feared, largely because many older people had some immunity to it.
The virus, called A/H1N1pdm09, is now covered by the annual flu vaccine to make sure people are protected.
The new flu strain that has been identified in China is similar to 2009 swine flu, but with some new changes.
So far, it hasn't posed a big threat, but Prof Kin-Chow Chang and colleagues who have been studying it, say it is one to keep an eye on.
The virus, which the researchers call G4 EA H1N1, can grow and multiply in the cells that line the human airways.
They found evidence of recent infection starting in people who worked in abattoirs and the swine industry in China.
Current flu vaccines do not appear to protect against it, although they could be adapted to do so if needed.
Prof Kin-Chow Chang, who works at Nottingham University in the UK, said "Right now we are distracted with coronavirus and rightly so. But we must not lose sight of potentially dangerous new viruses."
While this new virus is not an immediate problem, he says: "We should not ignore it."
Prof James Wood, head of the Department of Veterinary Medicine at the University of Cambridge, said the work "comes as a salutary reminder" that we are constantly at risk of new emergence of pathogens, and that farmed animals.
“Humans have greater contact than with wildlife, may act as the source for important pandemic viruses,” he added.